Means and method for producing a vacuum



Aug. 2, 1960 M. A. OTAVKA 2,947,465

MEANS AND METHOD F OR PRODUCING A VACUUM Filed May 20, 1958 T T V k" I J l '1 2,947,465 Patented Aug. 2, 1960 MEANS AND METHOD FOR PRODUCING A VACUUM Filed May 20, 1958, Ser. No. 736,650

6 Claims. Cl. 230-69) This invention relates to vacuum pumps and methods for producing vacuums. More particularly, this invention relates to vacuum pumps of the gettering type and methods of operation which are useful in producing high quality vacuums.

Getter type pumps depend primarily on the gettering action of materials such as titanium, zirconium, uranium, lithium, and tantalum for removing the presence of the common gases nitrogen, oxygen, hydrogen and the carbon oxides. This is done by evaporating the getter metal within the chamber to be evacuated. The evaporated metal coats the inside surfaces of the pump wall where the gettering of the gases takes place. To rid the vacuum chamber of inert gases, which are not subject to the gettering action, the electrons are caused to ionize the gases, and the positive ions formed thereby are subjected to an electric field which drives them into the metal coated wall.

One of the major problems which still exists preventing the widespread use of the gettertype pump is the difficulty in starting the operation. An electric potential is required between the filament and the element of the pump containing the titanium when the pump is started which may cause an ion discharge. In order to avoid the ion discharge the pressure within the chamber must be substantially reduced before any attempt can be made to heat the titanium to start the evaporation. Most mechanical vacuum pumps are not capable of producing such low pressures and the use of diffusion pumps as starters defeats the primary purpose of the development of the getter type pump. Diffusion pumps have a tendency to contaminate the evacuated chamber with oil or mercury depending on thetype of pump used. It is therefore an object of this invention to provide a high quality vacuum pump which may be started at pressures within the operating range of-existing mechanical pumps without the use of diffusion type pumps.

It is also an object of this invention to provide a vacuum pump of the gettering type which will not cause extensive gas ionization when its operation is first initiated.

Another object of this invention is to provide a method for reducing the gas pressure using a getter type pump wherein substantial gas ionization within the pump is eliminated when the operation of the pump is initiated.

The objects and advantages of this invention may best be accomplished in a device having a partially evacuated chamber with an element of a material such as the getter metals above mentioned capable of combining with the common gases, a filament surrounding the element and a grid surrounding the filament. An electric current is applied to the filament and a potential is applied to the grid so that substantially all the electrons emitted from the filament are directed towards the element to cause the getter material in the element to evaporate and deposit on the chamber walls, thereby providing the gettering action. The potential on the grid is then reversed when the pressure in the chamber is below the critical ion discharge value causing the inert gases to be ionized and the positive ions created thereby to be attracted to the chamber wall.

The invention may be better understood both as to its organization and method of operation from reference to the following specification taken in connection with the accompanying drawing which is a schematic view showing the general arrangement of the components of the pump with the associated electric potential circuit.

The vacuum pump 10 has a cylindrically shaped, electrically grounded chamber 12 formed of glass or metal or other substantially strong material capable of withstanding the pressures involved. Centrally located in the bottom portion of the chamber 12 is an element 14 containing a material which is capable of combining with the common gases through a gettering action wherein the material is evaporated and deposited on the inner Walls of the chamber as it absorbs the gases. A tantalum containing alloy such as Tantaloy, comprising Ta and 5% W is preferably used in the element. The element 14 is supported at its lower end by a structure 16 and has a grounded lead 18 extending through the chamber 12.

Surrounding the element 14 at its upper end is a filament 20 which is also supported by the structure 16 and is connected to a current supply which is not shown. The filament 20 is in close proximity to the element 14 and emits electrons when subjected to the electric current to heat the material in the element to cause it to evaporate.

A grid structure 22 is concentrically disposed between the walls of the chamber and the filament surrounded element 14. The grid structure 22 comprises two concentric commonly connected portions. One is disposed in close proximity to the wall of the chamber, extending the height of the chamber 12 and is referenced 26 in the drawing. The other portion 28 encircles the filament surrounded element 14 within the confines of the portion 26 and extends just above the top of the filament 20. The portions 26 and 28 are commonly connected to a lead 30 to a power supply 31 hereinafter described.

A second grid 32 comprising a loop of wires surrounds the element 14 between its supported lower end and its filament surrounded upper end, and is connected to the power supply 31 by lead 34.

The power supply 3 1 is a half-wave rectifier type circuit comprising a stepup transformer 36 with a rectifier 38, and a filter resistor 40 and capacitor 42- serially connected across the secondary thereof. The applicant uses ordinary electric light bulbs for the resistor 40 to provide a regulated output from the power supply 31. A reversing switch 44 around the capacitor 42 permits either plate of the capacitor 42 to be connected directly to ground through ammeter 46 while the other plate of the capacitor 42 is connected to the lead 30 from the grid structure 22. Thus either a positive or a negative voltage with respect to the grounded element 14 and chamber 12 may be selectively applied to the grid structrue 26. A center tapped resistor 48 serves as a bleeder and as a voltage divider for supplying a smaller voltage to the second grid 32.

To operate the pump the chamber 12 is first mechanically evacuated to a pressure between 10 -10 mm. mercury. An electric current is applied to the filament 20 and the switch 44 in the power supply 31. is positioned to place a negative potential on the grid structure 22. It will be noted that the second grid 32 is also placed at a negative potential with respect to the element 14 and reduces the effect on the electrons of any potential field present between the element 14 and the support structure 16. The material in the element 14 is caused to evaporate and deposit on the inner walls of the evacuation chamber 12 and combines with the common gases. Since most, of the electrons emitted from the filament 20 are iiestesi towar s the le t sle dise r eehse directing the hetnwaid the element lit] wete'hqt' Presen n he nressnie, W t in the ehemhe s. edne d b a e bi t e s e f ee n' h tithe ho en ei brehleihat ah the oten ial o t e id sthieth e 2 h r ver d t a the a in aet e so tha leyy's P eitiye val e.- Th e eet he mi ted r m th fihm ht a e thus treeted rew rds the id e et re nd in heh tehsnett se ne the. m eehlee' o e hi fre ase hesh t her 9 e i e in collisi ns t erewi h: i t. t r ed y he e ll s ens a e t rae ed embe Wal b mean o th p n l fie d h he Pos ve ent rtien 6 t h a st netht .2 and the. rounded e a nbe 1 p aet eihs i i e ion erp e n used. a se er yn uum ump o he p ma uf tured b G nel siated V pilum C pa y their model N 1 11 1, with modifications, as disclosed hreinahove. The pump pera ed i eee damee with e manuf t r s speeifi: ca ons elild e s art d only after'the p ure wa educed to between 1.2 to 1.8 1() mm. of mercury. By perat n th pum i a or an wi the nv ti n of h s ap a io oper w initiated a appr imate y lQ- mm. mercury which is within the operating range of existing mechanical pumps.

Whi e a par i ul em dimen of the in en on has n herei ab e. d crib d in d a l, i wi l e understood that there may be many modifications which may be included the scope of the invention. It is thereo e the nt n ion o h pplican to be bound n y within the limit of the appending claims.

What is claimed is: v

l. A method for reducing gas pressure in a partially evacuated chamber comprising heating a material capable of combining with the common gases Within the chamber by electron bombardment, While applying an electric potential field to cause substantially all of the electrons to be directed towards said material, reversing the electric field whereby the electrons are caused to ionize the gases within the chamber, and attracting the positive gas ions toward the walls of the chamber.

2. A method for reducing gas pressure using a getter type pump having a partially evacuated chamber, an element of a material capable of combining with the common gases in said chamber, a filament surrounding the element, and a grid surrounding the filament; comprising the steps, conducting an electric current through the filament, applying a negative potential to said grid with respect to said element and said chamber, and applying 4 a positive potential to said grid when the pressure in the chamber is below the critical glow-discharge value of the gases within the mann r;

3. A method for reducing gas pressure in a partially evacuated chamber comprising filament heating an element formed of a material capable of combining with the common gases within, the chamber, subjecting the en and e emen teaheiee ie ee en ie fi d whe substantially all of tlie elections emitted from the filament are directed toward the element causing said material to vapor z a d embiae with said ases .subiee hs he .fi f f m nt to an e t i potential field o ppo p arity when the pressure of the chamber is below the critical glow-dischargepoint, wherein some of the electrons emitted therefrom are directed'away from said element and cause ionization of the free gases within the chamber, the positive ions of said gases being attracted to the walls ofsaid chamber.

at Ap a atus e nr dae a ae e mnris ns -teens o m n a. artia ly eva u ed em ertan element havi g. mate al capab o eenib hi s the e m' qn ase e htra ly lbeeted Wit n s d am e and sun: ported at one end, an electron-emitting, heater filament sur ound n a e em n el se pro m ty to e 1 si pper es end o sa e me tr w e a i s r o nding sai amen w thin sa ehember, a reversible direct ur n powe supp y conne ted t sai gr d whereby the potential on said grid may be alternated between negative and positive with respect to said element and sa d hamb r 5. An apparatus as described in claim 4 comprising in addition a. second grid surrounding said element adjacent its supported end and connected to said reversible power supp y- 6. Apparatus for producing a vacuum comprising; means defining a partially evacuated chamber; an element having material capable of combining with the common gases centrally located within said chamber, an electron-emitting heater filament surrounding said element in close profiimity therewith, a wire grid surrounding said filament within said chamber, means for applying to said grid a negative potental with respect to said element and chamber, said applying means adaptable to apply a positive a potential to said grid when the pressure in the chamber is below the critical glow discharge value of the gases within the chamber.

References Cited the file of this patent UNITED TATE P TENTS 

